U.S. Pat. No. 4,183,383 discloses a wire lead forming machine of the general type to which the present invention relates, whereby each of a succession of cable lengths has a European-type two-pronged plug applied to one end of it while electrically connectable terminal leads are formed at its other end. That machine has a main conveyor comprising a pair of endless chains, each carrying wire clamps spaced at intervals along it. Horizontally extending and parallel top stretches of the respective chains, at opposite sides of the machine, move stepwise in unison to carry their wire clamps to each of a succession of stations along the length of the machine.
Successive lengths of two-conductor cable are delivered to the machine at an infeed end of it. They are oriented to extend transversely to the chains, and each cable length is gripped near its opposite ends by wire clamps on the respective chains. After each cable length is gripped by the wire clamps, it is brought to a station at which the outer insulating jacket is stripped off of each of its end portions, to expose end portions of the two insulated wires within that jacket. At a subsequent wire inserting station these end portions, at the plug end of the cable length, are engaged by one of a series of movable wire-controlling fixtures that are secured to an endless auxiliary conveyor. The auxiliary conveyor has a top stretch paralleling the top stretches of the main conveyor chains but extending along only a part of the length of the machine, and it moves in unison with the main conveyor.
At an actuating station after the wire inserting station, an actuator drivingly engages swingable parts of the movable wire controlling fixture, and the displacement of those parts bends the plug-end portions of the two wires to such configurations that, together, they define a U, with their tip portions parallel and spaced apart by a substantial distance in the direction of conveyor travel. The swingable parts of the movable fixture maintain their displaced setting to confine these end portions of the wires in the bent configuration as the fixture and cable length are carried through further stations. One of those further stations is a wire stripping station where insulation is removed from the tip portion of each wire by means of a pair of rotary devices, rotating side by side, each of which cuts through the insulation on one of the wires, grips the insulation, and pulls if off of the wire. Since the strippers rotate on fixed axes, the fixture that is carried by the auxiliary conveyor serves to hold the plug-end portions of the two wires in such positions and orientations that they are accurately coaxial with the rotary strippers and can be properly engaged by them for simultaneous insulation stripping.
From the wire stripping station the cable length is carried to a plug-attachment station where the stripped wire ends are inserted into tubular rear legs of plug prongs and those legs are crimped to secure them to the wires. At the plug-attachment station the movable fixture continues to maintain the plug-end portions of the wires in their bent configuration, ensuring that they will be located and oriented for accurately coaxial insertion into the tubular plug prong legs. Thereafter, as the conveyors move to a fixture resetting station, the plug end portion of the cable length is engaged by a ramp that lifts it out of the movable fixture, and at said resetting station the swingable parts of the fixture are reset back to their original condition. The subsequent orbital movement of the fixture with the auxiliary conveyor carries the movable fixture back towards the infeed end of the machine. Meanwhile, the cable length, with a plug now attached to it, moves on towards the discharge end of the machine, where it is released from the cable clamps on the main conveyor.
The wire-controlling movable fixtures on the auxiliary conveyor are relatively complicated and expensive devices. In their stepwise movement with the auxiliary conveyor they must be brought accurately into position at each of the fixture actuating, wire stripping, plug attaching and fixture resetting stations, and their swingable parts must be carefully made for precise cooperation with the mechanisms at those stations. The substantial cost of an individual fixture is multiplied by the relatively large number of such fixtures that must be attached to the auxiliary conveyor. Further cost is of course involved in the provision of the auxiliary conveyor itself and in the means for driving it in unison with the main conveyor and for indexing it for accurate positioning of every movable fixture at each station.
The machine of U.S. Pat. No. 4,183,383 has enjoyed substantial commercial success, so that there has been a great deal of practical experience with it. Thus the cost and complexity of the auxiliary conveyor and its multiplicity of wire controlling fixtures have been apparent for some time, but heretofore it has been far from obvious how to achieve a simplification and reduction of cost in the mechanism at the plug attaching side of the machine without loss of the reliability and versatility that are mandatory in such machines.
There would perhaps be relative little difficulty in simplifying a lead forming machine if it were intended only for use with relatively stiff wire that would maintain any configuration to which it might be bent. However, the type of cable to which a two-prong plug or the like is to be attached must ordinarily be so limp and supple that after being bent it has a tendency to return to straightness as soon as it is released. This suppleness or lack of memory in the wires of the cable poses one of the problems addressed by the present invention.
The wires must have their plug end portions bent apart for insulation stripping because they must be separated from one another for engagement by the rotary strippers. Conceivably the wires could be stripped one at a time, as is done at the opposite (terminal lead) side of the machine, and in that case the two wires would not have to be positioned and oriented with the accuracy that is needed for simultaneous insulation stripping. But when a cable length reaches the plug-attaching station, the plug-end portions of its wires must have a fairly accurate positioning and orientation, to ensure their simultaneous entry into the relatively narrow tubular legs of a plug. If the wires are not to be confined by means of a movable fixture that travels with them from station to station, then they must be brought to and maintained in the required positions and orientations by a reliable device that is stationarily located at the plug attachment station. And if no operation is performed upon the plug-end portions of the wires between the insulation stripping station and the plug attaching station, they will arrive at the latter in unpredictable positions and orientations, owing to their suppleness and tendency to straighten themselves. A reasonably simple and compact fixture at the plug attaching station could not assuredly bring whose wire end portions into accurate relationship to plug prongs if it had to be capable of receiving and engaging those wire portions in any of a wide range of possible positions and orientations.
Accurately positioning and orienting the plug end portions of the wires by means of a fixture or the like that is stationarily located at the plug attaching station poses another problem that has heretofore been rather baffling. With the movable wire controlling fixtures of U.S. Pat. No. 4,183,383, the bending of the plug-end portions of the wires could take place at a special setting station where an actuator could engage the movable fixture to shift its swingable parts for bending of the wire; and that actuator could be designed with little concern about its interference with the mechanisms for insulation stripping and for plug attachment inasmuch as such mechanisms were located at other stations, well spaced from the actuator. On the other hand, if the plug-end portions of the wires are to be bent and confined in a fixture or the like that is stationarily located at the plug attachment station, then neither that fixture nor the mechanism for actuating its movable parts should get between the tips of the wires and a plug to be attached to them, nor otherwise interfere with assembly of the wires and the plug. In effect, the whole of such a fixture and its actuating mechanism should be located at one side of a vertical plane that extends in the direction of conveyor movement and intersects the plug-end portions of the wires near their tips.